In recent years physicists have shown that DNA molecules, the building blocks of life, can exhibit semiconducting and superconducting properties. Now Yutaka Kawabe and colleagues at the Chitose Institute of Science and Technology in Hokkaido, Japan, have made a thin-film laser that contains DNA doped with dye molecules. When optically pumped, the film exhibits amplified spontaneous emission and spectral narrowing, which suggests that DNA complexes might be practical candidates for making solid-state-dye lasers (Y Kawabe et al 2002 Appl. Phys. Lett. 81 1372).
It is well known that placing too many dye molecules close together can lead to the quenching of fluorescence when pumped. The Chitose team has overcome this problem by using DNA as a scaffold that isolates the dye molecules and reduces the quenching. “If DNA makes other kinds of dye lase, the range of materials used in solid-state dye lasers will be greatly expanded,” say Kawabe and colleagues.
The scientists fabricate their films from a hemicyanine dye, a lipid and DNA. The ratio of DNA base pairs to dye molecules can be varied from 10:1 to 40:1, which results in films with thicknesses between a few microns and a few millimetres. A frequency-doubled Nd:YAG laser emitting nanosecond pulses optically pumps the film. The incident energy is varied up to a maximum of 1000 µJ.
An intensified CCD camera gathers the emission from the edge of the film and feeds it into a spectrometer. The authors observe spectral narrowing at threshold energies above 25 µJ and conclude that amplification has occurred.
Having tested their approach on a film that does not contain DNA, the researchers believe that the DNA plays an essential role in the laser action. Moreover, the performance of the laser only decreased by a few percent in two hours which, say Kawabe and colleagues, suggests that the device might be suitable for applications. Further studies of the structural and spectroscopic properties of the films are now being carried out.
